1  // Copyright (c) 2009-2010 Satoshi Nakamoto
 2  // Copyright (c) 2009-2020 The Bitcoin Core developers
 3  // Distributed under the MIT software license, see the accompanying
 4  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 5  
 6  #ifndef BITCOIN_FLATFILE_H
 7  #define BITCOIN_FLATFILE_H
 8  
 9  #include <string>
10  
11  #include <serialize.h>
12  #include <util/fs.h>
13  
14  struct FlatFilePos
15  {
16      int nFile{-1};
17      unsigned int nPos{0};
18  
19      SERIALIZE_METHODS(FlatFilePos, obj) { READWRITE(VARINT_MODE(obj.nFile, VarIntMode::NONNEGATIVE_SIGNED), VARINT(obj.nPos)); }
20  
21      FlatFilePos() {}
22  
23      FlatFilePos(int nFileIn, unsigned int nPosIn) :
24          nFile(nFileIn),
25          nPos(nPosIn)
26      {}
27  
28      friend bool operator==(const FlatFilePos &a, const FlatFilePos &b) {
29          return (a.nFile == b.nFile && a.nPos == b.nPos);
30      }
31  
32      friend bool operator!=(const FlatFilePos &a, const FlatFilePos &b) {
33          return !(a == b);
34      }
35  
36      bool IsNull() const { return (nFile == -1); }
37  
38      std::string ToString() const;
39  };
40  
41  /**
42   * FlatFileSeq represents a sequence of numbered files storing raw data. This class facilitates
43   * access to and efficient management of these files.
44   */
45  class FlatFileSeq
46  {
47  private:
48      const fs::path m_dir;
49      const char* const m_prefix;
50      const size_t m_chunk_size;
51  
52  public:
53      /**
54       * Constructor
55       *
56       * @param dir The base directory that all files live in.
57       * @param prefix A short prefix given to all file names.
58       * @param chunk_size Disk space is pre-allocated in multiples of this amount.
59       */
60      FlatFileSeq(fs::path dir, const char* prefix, size_t chunk_size);
61  
62      /** Get the name of the file at the given position. */
63      fs::path FileName(const FlatFilePos& pos) const;
64  
65      /** Open a handle to the file at the given position. */
66      FILE* Open(const FlatFilePos& pos, bool read_only = false);
67  
68      /**
69       * Allocate additional space in a file after the given starting position. The amount allocated
70       * will be the minimum multiple of the sequence chunk size greater than add_size.
71       *
72       * @param[in] pos The starting position that bytes will be allocated after.
73       * @param[in] add_size The minimum number of bytes to be allocated.
74       * @param[out] out_of_space Whether the allocation failed due to insufficient disk space.
75       * @return The number of bytes successfully allocated.
76       */
77      size_t Allocate(const FlatFilePos& pos, size_t add_size, bool& out_of_space);
78  
79      /**
80       * Commit a file to disk, and optionally truncate off extra pre-allocated bytes if final.
81       *
82       * @param[in] pos The first unwritten position in the file to be flushed.
83       * @param[in] finalize True if no more data will be written to this file.
84       * @return true on success, false on failure.
85       */
86      bool Flush(const FlatFilePos& pos, bool finalize = false);
87  };
88  
89  #endif // BITCOIN_FLATFILE_H